The present invention relates to a hydraulic engine mount, i.e., a hydramount, including a supporting bearing and a bearing member, which are supported on each other by an essentially frustoconical, first elastic spring element made of an elastomer material, and including a working chamber and a compensating chamber, which are each filled with hydraulic fluid, are separated from each other by a partition, and are in fluid communication via a first damping opening.
Such hydramounts are described, for example, in German Published Patent Application No. 41 41 332. Conventional hydramounts are especially used as engine, gearing or transmission suspensions in motor vehicles. The action of these hydramounts is substantially axial, in the direction of the hydramount, liquid constituents being displaced back and forth through the damping opening, between the working chamber and the compensating chamber, in order to damp low-frequency, high-amplitude engine vibrations. High-frequency, low-amplitude vibrations, e.g., vibrations induced by the internal combustion engine itself, are isolated by a diaphragm, which is made of an elastomer material and is mounted inside the partition so as to be capable of vibrating.
In the radial direction of the hydramount, supporting action is substantially attained by locally hard, rubber spring segments, while isolation is provided by locally soft, rubber spring segments. This variable adjustment of the first elastic spring element to different requirements renders the cost of developing appropriate elastomer springs high. Nevertheless, the result is generally a compromise, because only the material of the elastic spring element damps in the radial direction. The choice of suitable materials is very limited since, to achieve effective axial damping action, materials that have a very low damping capability and only harden to a small extent are necessary for the first elastic spring element.
It is an object of the present invention to provide a hydramount that, in addition to the improved working properties of the hydramount in the axial direction, improved working properties may also be attained in regard to the damping in the radial direction.
The above and other beneficial objects of the present invention are achieved by providing that the supporting bearing is in the form of an internal, first supporting body, which is enclosed by an external, second supporting body at a radial distance, that the first and second supporting bodies are connected by the first elastic spring element and a second elastic spring element, that the first and the second supporting bodies delimit at least two chambers filled with hydraulic fluid, and that the chambers are positioned perpendicularly to the axis, substantially in diametric opposition to each other in the radial direction, and are in fluid communication via at least one second damping opening. The hydramount according to the present invention includes the advantage of possessing, on one hand, the usual working properties with regard to the damping and the isolation of vibrations in the axial direction, and on the other hand, an improved damping effect in the radial direction, i.e., perpendicularly to the axis. The additional configuration of the chamber pair, in which the two chambers of the chamber pair are in fluid communication via the second damping opening, also allows low-frequency, high-amplitude vibrations to be damped in the radial direction.
For example, damping in the radial direction is necessary in order to damp pitching motions of an engine mounted longitudinally in a motor vehicle. Engine shaking motions in transversely mounted engines may also be effectively damped by the hydramount damping that acts in the radial direction. Depending on the particular application case and the design of the second throttle opening, there is also the possibility of isolating shaking motions of the engine, using an absorption effect. The dynamic reduction in stiffness caused by the absorption effect allows comparatively high radial spring constants for supporting the engine in the direction of travel, e.g., while accelerating and braking, which is very improved for the driving comfort.
Engine shaking motions in engines mounted longitudinally in motor vehicles may be damped by the hydramount according to the present invention, in the transverse direction of the vehicle, or they may be isolated by an absorption effect when the second damping opening is appropriately designed. In the case of absorbing vibrations, the cornering performance of a motor vehicle can be improved by a higher static spring constant. That is, the engine does not strike the end stop too early in the radial direction, which means that the noise is minimized, and reverberation, e.g., post-vibration of the engine is prevented in the transverse direction.
Therefore, the improved working properties result from integrating at least one additional chamber pair, e.g., in the form of a hydraulic sleeve, into a conventional hydramount, the additional chamber pair acting in the radial direction.
The second supporting body and the bearing member may be formed from a uniform material and/or may be formed in one piece. The one-piece design allows the hydramount to be manufactured inexpensively and to be assembled from a small number of parts. However, if the second supporting body and the bearing member are formed in two pieces, then undercuts may be produced in the radial direction. When removing the part from the vulcanization tool, neither the part itself nor the tool is damaged/destroyed.
The first and the second elastic spring elements may be formed in one piece or multiple pieces. The one-piece design of the two elastic spring elements allows the hydramount to be manufactured easily and inexpensively, the choice of material depending mainly on the required spring stiffnesses of the elastic spring elements.
For example, the first damping opening may be designed in the shape of a channel and may form the circumference of the partition. In this connection, it may be advantageous that the comparatively large channel length of the damping opening allows a large mass of fluid to vibrate back and forth between the working chamber and the compensating chamber and therefore allows low-frequency, high-amplitude vibrations to be damped effectively.
The second damping opening may be in the form of a choke, a throttle or an absorption channel. If the second damping opening is in the form of a throttle, the radially induced vibrations are damped by forcing hydraulic fluid between the chambers of the chamber pairs, through the second damping opening having a comparatively small cross-section. A condition for the throttle damping is that the chamber walls should be very resistant to inflation. This is achieved by short, thick spring segments made of elastomer. The second damping opening may also be in the form of an absorption channel. In this context, the length of the damping opening is small, and its cross-section is large, in order to attain a dynamic stiffness in the frequency range of 20 to 80 Hz, which is lower than the static stiffness. A plurality of absorption channels may be arranged in a functionally parallel circuit.
The first and the second elastic spring elements may define two chamber pairs, which are positioned adjacently to each other in the axial direction, the chambers of each chamber pair being positioned transversely to the axis, substantially in diametric opposition to each other in the radial direction, and being in fluid communication with each other, and the chamber pairs being positioned so as to be offset 90xc2x0 from each other. Vibrations may be damped in all three spatial directions. In the application case of a motor vehicle, this means that vibrations may be damped in the travel direction, transversely to the travel direction, and perpendicularly to the road surface. In this case, the degree of undesirable vibration transmission, e.g., into the passenger compartment of the motor vehicle, is particularly small.
The second elastic spring element may be disposed on the side of the first elastic spring element facing away from the working chamber. The first elastic spring element, the supporting bearing, the bearing member, and the partition delimit the working chamber. This arrangement allows a high degree of damping in the axial direction of the hydramount, since, due to the higher spring stiffness in comparison with the second elastic spring element, the first elastic spring element""s pumping action on the hydraulic fluid in the working chamber is improved.
However, in general, there is also the possibility of positioning the second elastic spring element on the side of the first elastic spring element facing the working chamber. The arrangement of the second elastic spring element inside the hydramount reliably protects the thinner, second elastic spring element from outside influences. This arrangement minimizes the danger of being damaged. The chambers of the chamber pair, which are filled with hydraulic fluid, are disposed in the axial space between the two elastic spring elements.
The second elastic spring element may substantially be formed in the shape of a rolling diaphragm. In response to elastic deflection and rebounding in the axial direction, and in response to the inner supporting body being radially shifted with respect to the outer supporting body, tensile stresses inside the second elastic spring element, which are harmful and reduce the service life, are reliably prevented by the rolling-diaphragm-shaped design of the second elastic spring element. In this manner, the hydramount exhibits uniformly improved working properties during a long service life.
When viewed in longitudinal section, the second elastic spring element has a smaller sectional area than the first elastic spring element. For safety reasons, the part-rubber, part-metal construction may include a rigid, conical first elastic spring element, which may bear the static loading alone. In conjunction with the inflation resistance of the first elastic spring element, the second elastic spring element includes the necessary inflation resistance for the damping/absorption in the radial direction of the hydramount.
The second damping opening may be radially positioned between the second supporting body and the chambers. Because the second damping opening for the radial action of the hydramount may be situated in the region of the outer supporting body, the large length of the damping opening and a large cross-section may generate a high degree of damping at a low volumetric stiffness of the chambers. In this manner, the degree of dynamic hardening of the hydramount remains low. The second damping opening may be situated in the region of the chambers, either with or without additional component parts. In addition, there is the possibility of directing the channels underneath the chambers, between the outer supporting body and the bearing member.
According to another aspect of the present invention, there is the possibility of radially positioning the second damping opening between the first supporting body and the chambers. In this case, the length of the second damping opening may be comparatively small, and its cross-section may be large, in order to absorb vibration. In the case of vibration absorption in a frequency range of 20 to 80 Hz, a dynamic stiffness is achieved that is less than the static stiffness.
Spring configurations, which have a first and a second elastic spring element and chambers between them, and provide damping in the radial direction by means of openings, may also be combined with a third opening between the axially acting working chamber and the compensating chamber, a first control element opening or closing this third opening as a function of the operating state of the vehicle. Opening it causes a mass of liquid to vibrate in the opening, which has the effect of hydraulically absorbing vibration in order to reduce the dynamic stiffness of the mount in the axial direction. In this context, the adjusting element may operate electrically, as well as hydraulically or pneumatically.
Closing the third opening produces the action of a conventional, hydraulically damping mount, along with the advantage of radial damping.
A prerequisite for the above-mentioned absorbing action is either a rigid wall between the working chamber and the compensating chamber, or at least a supported, but inflatable or expandable diaphragm between two grating regions. To improve the acoustics, it may be advantageous to position this diaphragm between the gratings so as to be able to move. Using a movable grating, the diaphragm must then be clamped when the third opening is open and be provided with free space when the third opening is closed.
The freely movable diaphragm allows the dynamic stiffness to be reduced considerably in the acoustically active frequency range.
The movable grating may be actuated by the first control element, which also releases the third opening.
Since hydraulically damping mounts in motor vehicles are normally set at an angle when they are installed, and idling internal combustion engines not only undergo movements in the cylinder direction, but also in the direction perpendicular to it, it may be advantageous to isolate these as well, in order to provide improved vibrational comfort. In order to achieve this result, either a short channel is connected to the damping channel between the radially acting chambers, between the first and second elastic spring elements, or the channel is shortened. This arrangement may be achieved by a second control element, which operates electrically, pneumatically, or hydraulically.